class_docstr: Customed Graph class.
docstr: Reutn number of layer.
docstr_tok: ["Reutn","number","of","layer","."]
code: def layer_num(self, layers=None):
      """
      Reutn number of layer.
      """
      if layers is None:
          layers = self.layers
      layer_num = 0
      for layer in layers:
          if (
              layer.is_delete is False
              and layer.graph_type != LayerType.input.value
              and layer.graph_type != LayerType.output.value
          ):
              layer_num += 1
      return layer_num
  
imports: import copy
  import hashlib
  import logging
  import json
  import random
  from collections import deque
  from enum import Enum, unique
  from typing import Iterable
  import numpy
label_desc: Use image node_id 3 for calling the Graph obj's underlying member method code with example usage: obj.layer_num(layers) and returns: layer_num